过去完成时“五步曲”
一、 过去完成时的概念与结构特点过去完成时表示在过去某一时间或动作之前已经发生或完成了的动作，即“过去的过去”（past-in-the-past）。
二、 过去完成时的构成
(1)过去完成时由“助动词had + 动词的`过去分词”构成，其中had通用于各种人称。例如：
They had already had breakfast before they arrived at the hotel.
She had finished writing the composition by 10:00 this morning.
(2)过去完成时的否定形式由主语+助动词had + not +动词的过去分词构成 ，例如：
They hadn’t already had breakfast before they arrived at the hotel.
She hadn’t finished writing the composition by 10:00 this morning
(3)其一般疑问句把had放于句首，即Had+主语+动词的过去分词。
Had they already had breakfast before they arrived at the hotel?
Had she finished writing the composition by 10:00 this morning?
三、 与过去完成时连用的时间状语
1) by+ 过去时间点
如：I had finished reading the novel by nine o’clock last night.
2) by the end of +过去时间点
如：We had learned over two thousand English words by the end of last month.
3) by the time +从句（一般过去时），主句（过去完成时）
如: The train had left by the time I got to station. 4) 用于由when ,after , before 引导的时间状语从句中，前后两动作都发生在过去。
过去完成时+when/before +一般过去时
一般过去时+after +过去完成时
如：When I got home, my mother had had dinner already.
They had planted six hundred trees before last Sunday.
After he had finished his homework , he went to bed.
四、 用于宾语从句结构中的过去完成时
当宾语从句中的主句为一般过去时，且从句的动作先于主句的动作时，从句要用过去完成时。在told, said, knew, heard, thought 等动词后的宾语从句中。如：
She said that she had seen the film before.
五、 过去完成时与现在完成时的区别
现在完成时表示的动作发生在过去，但侧重对现在造成的影响或结果与现在有关，其结构为“have/has+动词的过去分词”，过去完成时则是一个相对的时态 ，它所表示的动作不仅发生在过去，更强调“过去的过去”，只有和过去某动作比较时，才用到它。试比较：
I have learned 1000 English words so far. 到目前为止我已经学会了1000个单词。
I had learned 1000 English words till then. 到那时为止我已经学会了1000个单词。